The present invention relates generally to a method and system for making optical measurements and, more particularly, to a method and system for making optical measurements using optical coherence domain reflectometry.
Optical coherence domain reflectometry (OCDR), a well known technique, is based on detection of an interference signal and becomes an attractive method for making precision measurements that provides resolution of 10 um and a dynamic range of more than 100 dB for depth scan up to few mm. Using a high speed linear translation stage, OCDR measurements can be performed at modest high speeds. This method can be used to determine an internal depth image below the surface. OCDR has been developed for imaging of the anterior eye and retina, optical tomography and histology in highly-scattering media, and catheter-endoscope tomography in internal organ systems. The mirror velocity is typically in the range of 30 mm/sec corresponding to a Doppler frequency of 50 kHz. To achieve ultrahigh image acquisition speeds alternative technologies to mirror-translation scanning must be developed.
In U.S. Pat. No. 4,459,570 issued on Oct. 17, 1995 to E. A. Swanson et. al, a method and apparatus for performing various optical measurements is provided utilizing an optical coherence domain refractometer (OCDR). A short coherence optical radiation source applies optical radiation through like optical paths to a sample and an optical reflector. The optical reflector is movable in accordance with a predetermined velocity profile to permit interferometric scanning of the sample, the resulting output having a Doppler shift frequency modulation. This output may be demodulated and detected to obtain desired measurements and other information. Additional information may be obtained by applying radiation from two or more sources at different wavelengths to the sample and reflector and by separately demodulating the resulting outputs before processing. Birefringent information may be obtained by polarizing the optical radiation used, by suitably modifying the polarization in the sample and reference paths and by dividing the output into orthogonal polarization outputs which are separately demodulated before processing.
Another reference of interest is U.S. Pat. No. 5,491,552 issued on Feb. 13, 1996 to A. Knuttel.
It is an object of this invention to provide a new and improved method and system for optically performing high resolution measurements.
It is another object of this invention to provide a new and improved method and system for optically performing high resolution measurements using a diffraction grating.
It is another object of this invention to provide a method and system for obtaining a 2D image of a sample without scanning the sample in the lateral direction.
It is a further object of this invention to provide a method and system for obtaining a 3D image of a sample.